1. Field of the Invention
The present invention relates to a dental implant including a dental implant fixture and an abutment fitted and fixed in the dental implant fixture, only the abutment being removable for replacement while the dental implant fixture is being left fitted and fixed in place in an implanting hole made in the jawbone even at occurrence of a trouble such as damage to a broken dental prosthesis, fracture of a portion of the abutment to which the dental prosthesis is fixed or the like.
2. Description of the Conventional Art
In the field of dental therapy, there have been developed dental implant techniques in which an implanting hole is formed in a portion of the jawbone where a natural tooth is missing, a dental implant fixture to keep a dental prosthesis is placed in the implanting hole to work instead of the root of a natural tooth, an abutment as a first upper structural member is installed directly to the oral cavity-side end of the dental implant fixture, a dental prosthesis fixing device as a second upper structural member is fixed to the abutment to provide a dental prosthesis retaining device and a dental prosthesis is attached to the dental prosthesis retaining device.
As one of the dental treatment techniques, there is mainly adopted a dental implanting method called “two-stage process”. In this method, the following is done:
a dental implant fixture is placed in an implanting hole formed in a portion of the jawbone where a natural tooth is missing;
the oral cavity-side end of the dental implant fixture is covered with a cover screw;
the gingival flap having been cut out for drilling the implanting hole in the jawbone is stitched closed;
a certain healing period is set for which an integration of the dental implant fixture with the surrounding bone, called “osseointegration”, will be attained so that the dental implant fixture will be sufficiently integrated with the jawbone portion corresponding to the missing tooth and the gum tissue cut out for forming the implanting hole will heal;
after completion of the healing period, it is checked that the dental implant fixture is sufficiently integrated with the jawbone and the gum tissue has healed;
an incision is made again in an oral cavity-side portion of the gum tissue in which the dental implant fixture is placed and the cover screw is removed;
a healing abutment is installed to the oral-cavity end of the dental implant fixture;
a hole is made and kept in the gum for fixing through it an abutment as a first upper structural member having a portion on which a dental prosthesis fixing device is to be mounted;
another healing period for which the gum will heal is set; after completion of this healing time, it is checked that the gum has healed; and
the abutment is finally fixed in the hole.
Recently, in addition to the above-mentioned two-stage process, there has also become employed a dental implanting method called “single-stage process” in which immediately after a dental implant fixture is placed in an implanting hole formed in a jawbone portion where a natural tooth is missing, a healing abutment or an abutment is installed to the oral cavity-side end of the dental implant fixture. Namely, no surgery is done for exteriorizing the cover screw as at the second stage of the two-stage process. This one-stage process has been adopted more and more because both the patient and dental surgeon bear less; however, it has a high risk for infection in case bone argumentation is required because the jawbone is not enough in height and thickness to place a dental implant.
Both the above processes (especially the two-stage process) frequently use a dental implant fixture which is internally threaded and an abutment which is externally threaded. Namely, the abutment is fixed to the dental implant fixture by threading the former into the latter. Such a technique is disclosed in the Japanese Published Unexamined Application No. 113718 of 2004, for example. For such fixing of the abutment to the dental implant fixture by threading, however, a through-hole for a fixation screw has to be formed in the abutment. Especially, in case the abutment used is an order-made one manufactured with the use of a CAD/CAM system, designing such an order-made abutment is limited by the necessity of the through hole for the fixation screw. Particularly, in case the dental prosthesis fixing device as a second upper structural member to be fixed to the abutment has a small external form, the portion of the abutment to which the dental prosthesis fixing device is to be fixed should be thin. Also, if priority is given to forming the through hole for the fixation screw, the abutment cannot be formed to have any portion large enough to receive and fix the dental prosthesis fixing device. Further, even if it is barely possible to design an abutment having a portion to which the dental prosthesis fixing device can be fixed, the dental prosthesis cannot be formed sufficiently thick in many cases. Consequently, there are problems that no satisfactory strength and color can be imparted to the dental prosthesis.
Also, there has been proposed an integral type dental appliance formed from an integration of a dental implant fixture and abutment. This is disclosed in the Japanese Published Unexamined Application No. 329244 of 2005, for example. Also in the dental appliance of such an integral type, however, a portion of the dental appliance corresponding to the abutment to which the dental prosthesis fixing device is to be fixed cannot be formed thin since it is necessary to form, in the abutment portion of the dental appliance, a relatively large engagement hole in which there is to be inserted a tool for placing the dental appliance in an implanting hole formed in a jawbone portion corresponding to a missing tooth. Even if it is barely possible to form a thin portion of the dental appliance corresponding to the abutment, the dental prosthesis cannot be designed sufficiently thick many cases. Thus, there remains unsolved a problem that no satisfactory strength and color can be imparted to the dental prosthesis. Also, the integral type dental appliance is seriously disadvantageous in that at occurrence of a trouble such as damage to a dental prosthesis fixed to a dental prosthesis fixing device, fracture of a portion of the appliance to which the dental prosthesis fixing device is to be fixed or the like in the process of an implant surgery in which the dental prosthesis fixing device fixed to the integrated type dental appliance is used as a dental prosthesis retaining device and the dental prosthesis is fixed to the dental prosthesis fixing device, the dental appliance itself becomes unusable and another implant surgery has to be retried from the beginning.